#include"stdio.h"
int main()
{
int k;
scanf("%d",&k);
int arr[] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
int sz = sizeof(arr) / sizeof(arr[0]);
int left = 0;
int right = sz - 1;
   while(left <= right)
   {
int mid = (left + right) / 2;
    if (arr[mid] < k)
     { 
   left = mid + 1;
     }
    else if(arr[mid] > k)
      {
   right = mid - 1;
      }
    else
       { 
     printf("找到下标为:%d\n",mid);
break;
       }
   }
         if(left > right)
printf("找不到");
return 0;
}